/**
 * Licensed to the Apache Software Foundation (ASF) under one
 * or more contributor license agreements.  See the NOTICE file
 * distributed with this work for additional information
 * regarding copyright ownership.  The ASF licenses this file
 * to you under the Apache License, Version 2.0 (the
 * "License"); you may not use this file except in compliance
 * with the License.  You may obtain a copy of the License at
 *
 * http://www.apache.org/licenses/LICENSE-2.0
 *
 * Unless required by applicable law or agreed to in writing, software
 * distributed under the License is distributed on an "AS IS" BASIS,
 * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
 * See the License for the specific language governing permissions and
 * limitations under the License.
 */
package org.apache.hadoop.hbase.procedure2;

import java.io.IOException;
import java.util.Arrays;
import java.util.List;
import java.util.Map;

import org.apache.hadoop.hbase.exceptions.TimeoutIOException;
import org.apache.hadoop.hbase.metrics.Counter;
import org.apache.hadoop.hbase.metrics.Histogram;
import org.apache.hadoop.hbase.procedure2.store.ProcedureStore;
import org.apache.hadoop.hbase.procedure2.util.StringUtils;
import org.apache.hadoop.hbase.security.User;
import org.apache.hadoop.hbase.util.EnvironmentEdgeManager;
import org.apache.hadoop.hbase.util.NonceKey;
import org.apache.yetus.audience.InterfaceAudience;
import org.slf4j.Logger;
import org.slf4j.LoggerFactory;

import org.apache.hbase.thirdparty.com.google.common.annotations.VisibleForTesting;

import org.apache.hadoop.hbase.shaded.protobuf.generated.ProcedureProtos.ProcedureState;

/**
 * Base Procedure class responsible for Procedure Metadata; e.g. state, submittedTime, lastUpdate,
 * stack-indexes, etc.
 * <p/>
 * Procedures are run by a {@link ProcedureExecutor} instance. They are submitted and then the
 * ProcedureExecutor keeps calling {@link #execute(Object)} until the Procedure is done. Execute may
 * be called multiple times in the case of failure or a restart, so code must be idempotent. The
 * return from an execute call is either: null to indicate we are done; ourself if there is more to
 * do; or, a set of sub-procedures that need to be run to completion before the framework resumes
 * our execution.
 * <p/>
 * The ProcedureExecutor keeps its notion of Procedure State in the Procedure itself; e.g. it stamps
 * the Procedure as INITIALIZING, RUNNABLE, SUCCESS, etc. Here are some of the States defined in the
 * ProcedureState enum from protos:
 * <ul>
 * <li>{@link #isFailed()} A procedure has executed at least once and has failed. The procedure may
 * or may not have rolled back yet. Any procedure in FAILED state will be eventually moved to
 * ROLLEDBACK state.</li>
 * <li>{@link #isSuccess()} A procedure is completed successfully without exception.</li>
 * <li>{@link #isFinished()} As a procedure in FAILED state will be tried forever for rollback, only
 * condition when scheduler/ executor will drop procedure from further processing is when procedure
 * state is ROLLEDBACK or isSuccess() returns true. This is a terminal state of the procedure.</li>
 * <li>{@link #isWaiting()} - Procedure is in one of the two waiting states
 * ({@link ProcedureState#WAITING}, {@link ProcedureState#WAITING_TIMEOUT}).</li>
 * </ul>
 * NOTE: These states are of the ProcedureExecutor. Procedure implementations in turn can keep their
 * own state. This can lead to confusion. Try to keep the two distinct.
 * <p/>
 * rollback() is called when the procedure or one of the sub-procedures has failed. The rollback
 * step is supposed to cleanup the resources created during the execute() step. In case of failure
 * and restart, rollback() may be called multiple times, so again the code must be idempotent.
 * <p/>
 * Procedure can be made respect a locking regime. It has acquire/release methods as well as an
 * {@link #hasLock()}. The lock implementation is up to the implementor. If an entity needs to be
 * locked for the life of a procedure -- not just the calls to execute -- then implementations
 * should say so with the {@link #holdLock(Object)} method.
 * <p/>
 * And since we need to restore the lock when restarting to keep the logic correct(HBASE-20846), the
 * implementation is a bit tricky so we add some comments hrre about it.
 * <ul>
 * <li>Make {@link #hasLock()} method final, and add a {@link #locked} field in Procedure to record
 * whether we have the lock. We will set it to {@code true} in
 * {@link #doAcquireLock(Object, ProcedureStore)} and to {@code false} in
 * {@link #doReleaseLock(Object, ProcedureStore)}. The sub classes do not need to manage it any
 * more.</li>
 * <li>Also added a locked field in the proto message. When storing, the field will be set according
 * to the return value of {@link #hasLock()}. And when loading, there is a new field in Procedure
 * called {@link #lockedWhenLoading}. We will set it to {@code true} if the locked field in proto
 * message is {@code true}.</li>
 * <li>The reason why we can not set the {@link #locked} field directly to {@code true} by calling
 * {@link #doAcquireLock(Object, ProcedureStore)} is that, during initialization, most procedures
 * need to wait until master is initialized. So the solution here is that, we introduced a new
 * method called {@link #waitInitialized(Object)} in Procedure, and move the wait master initialized
 * related code from {@link #acquireLock(Object)} to this method. And we added a restoreLock method
 * to Procedure, if {@link #lockedWhenLoading} is {@code true}, we will call the
 * {@link #acquireLock(Object)} to get the lock, but do not set {@link #locked} to true. And later
 * when we call {@link #doAcquireLock(Object, ProcedureStore)} and pass the
 * {@link #waitInitialized(Object)} check, we will test {@link #lockedWhenLoading}, if it is
 * {@code true}, when we just set the {@link #locked} field to true and return, without actually
 * calling the {@link #acquireLock(Object)} method since we have already called it once.</li>
 * </ul>
 * <p/>
 * Procedures can be suspended or put in wait state with a callback that gets executed on
 * Procedure-specified timeout. See {@link #setTimeout(int)}}, and
 * {@link #setTimeoutFailure(Object)}. See TestProcedureEvents and the TestTimeoutEventProcedure
 * class for an example usage.
 * </p>
 * <p/>
 * There are hooks for collecting metrics on submit of the procedure and on finish. See
 * {@link #updateMetricsOnSubmit(Object)} and {@link #updateMetricsOnFinish(Object, long, boolean)}.
 */
@InterfaceAudience.Private
public abstract class Procedure<TEnvironment> implements Comparable<Procedure<TEnvironment>> {
    private static final Logger LOG = LoggerFactory.getLogger(Procedure.class);
    public static final long NO_PROC_ID = -1;
    protected static final int NO_TIMEOUT = -1;

    public enum LockState {
        LOCK_ACQUIRED,       // Lock acquired and ready to execute
        LOCK_YIELD_WAIT,     // Lock not acquired, framework needs to yield
        LOCK_EVENT_WAIT,     // Lock not acquired, an event will yield the procedure
    }

    // Unchanged after initialization
    private NonceKey nonceKey = null;
    private String owner = null;
    private long parentProcId = NO_PROC_ID;
    private long rootProcId = NO_PROC_ID;
    private long procId = NO_PROC_ID;
    private long submittedTime;

    // Runtime state, updated every operation
    private ProcedureState state = ProcedureState.INITIALIZING;
    private RemoteProcedureException exception = null;
    private int[] stackIndexes = null;
    private int childrenLatch = 0;

    private volatile int timeout = NO_TIMEOUT;
    private volatile long lastUpdate;

    private volatile byte[] result = null;

    private volatile boolean locked = false;

    private boolean lockedWhenLoading = false;

    /**
     * Used for override complete of the procedure without actually doing any logic in the procedure.
     * If bypass is set to true, when executing it will return null when
     * {@link #doExecute(Object)} is called to finish the procedure and release any locks
     * it may currently hold. The bypass does cleanup around the Procedure as far as the
     * Procedure framework is concerned. It does not clean any internal state that the
     * Procedure's themselves may have set. That is for the Procedures to do themselves
     * when bypass is called. They should override bypass and do their cleanup in the
     * overridden bypass method (be sure to call the parent bypass to ensure proper
     * processing).
     * <p></p>Bypassing a procedure is not like aborting. Aborting a procedure will trigger
     * a rollback. And since the {@link #abort(Object)} method is overrideable
     * Some procedures may have chosen to ignore the aborting.
     */
    private volatile boolean bypass = false;

    /**
     * Indicate whether we need to persist the procedure to ProcedureStore after execution. Default to
     * true, and the implementation can all {@link #skipPersistence()} to let the framework skip the
     * persistence of the procedure.
     * <p/>
     * This is useful when the procedure is in error and you want to retry later. The retry interval
     * and the number of retries are usually not critical so skip the persistence can save some
     * resources, and also speed up the restart processing.
     * <p/>
     * Notice that this value will be reset to true every time before execution. And when rolling back
     * we do not test this value.
     */
    private boolean persist = true;

    public boolean isBypass() {
        return bypass;
    }

    /**
     * Set the bypass to true.
     * Only called in {@link ProcedureExecutor#bypassProcedure(long, long, boolean, boolean)} for now.
     * DO NOT use this method alone, since we can't just bypass one single procedure. We need to
     * bypass its ancestor too. If your Procedure has set state, it needs to undo it in here.
     * @param env Current environment. May be null because of context; e.g. pretty-printing
     *            procedure WALs where there is no 'environment' (and where Procedures that require
     *            an 'environment' won't be run.
     */
    protected void bypass(TEnvironment env) {
        this.bypass = true;
    }

    boolean needPersistence() {
        return persist;
    }

    void resetPersistence() {
        persist = true;
    }

    protected final void skipPersistence() {
        persist = false;
    }

    /**
     * The main code of the procedure. It must be idempotent since execute()
     * may be called multiple times in case of machine failure in the middle
     * of the execution.
     * @param env the environment passed to the ProcedureExecutor
     * @return a set of sub-procedures to run or ourselves if there is more work to do or null if the
     *         procedure is done.
     * @throws ProcedureYieldException the procedure will be added back to the queue and retried
     *         later.
     * @throws InterruptedException the procedure will be added back to the queue and retried later.
     * @throws ProcedureSuspendedException Signal to the executor that Procedure has suspended itself
     *         and has set itself up waiting for an external event to wake it back up again.
     */
    protected abstract Procedure<TEnvironment>[] execute(
            TEnvironment env) throws ProcedureYieldException, ProcedureSuspendedException, InterruptedException;

    /**
     * The code to undo what was done by the execute() code.
     * It is called when the procedure or one of the sub-procedures failed or an
     * abort was requested. It should cleanup all the resources created by
     * the execute() call. The implementation must be idempotent since rollback()
     * may be called multiple time in case of machine failure in the middle
     * of the execution.
     * @param env the environment passed to the ProcedureExecutor
     * @throws IOException temporary failure, the rollback will retry later
     * @throws InterruptedException the procedure will be added back to the queue and retried later
     */
    protected abstract void rollback(TEnvironment env) throws IOException, InterruptedException;

    /**
     * The abort() call is asynchronous and each procedure must decide how to deal
     * with it, if they want to be abortable. The simplest implementation
     * is to have an AtomicBoolean set in the abort() method and then the execute()
     * will check if the abort flag is set or not.
     * abort() may be called multiple times from the client, so the implementation
     * must be idempotent.
     *
     * <p>NOTE: abort() is not like Thread.interrupt(). It is just a notification
     * that allows the procedure implementor abort.
     */
    protected abstract boolean abort(TEnvironment env);

    /**
     * The user-level code of the procedure may have some state to
     * persist (e.g. input arguments or current position in the processing state) to
     * be able to resume on failure.
     * @param serializer stores the serializable state
     */
    protected abstract void serializeStateData(ProcedureStateSerializer serializer) throws IOException;

    /**
     * Called on store load to allow the user to decode the previously serialized
     * state.
     * @param serializer contains the serialized state
     */
    protected abstract void deserializeStateData(ProcedureStateSerializer serializer) throws IOException;

    /**
     * The {@link #doAcquireLock(Object, ProcedureStore)} will be split into two steps, first, it will
     * call us to determine whether we need to wait for initialization, second, it will call
     * {@link #acquireLock(Object)} to actually handle the lock for this procedure.
     * <p/>
     * This is because that when master restarts, we need to restore the lock state for all the
     * procedures to not break the semantic if {@link #holdLock(Object)} is true. But the
     * {@link ProcedureExecutor} will be started before the master finish initialization(as it is part
     * of the initialization!), so we need to split the code into two steps, and when restore, we just
     * restore the lock part and ignore the waitInitialized part. Otherwise there will be dead lock.
     * @return true means we need to wait until the environment has been initialized, otherwise true.
     */
    protected boolean waitInitialized(TEnvironment env) {
        return false;
    }

    /**
     * The user should override this method if they need a lock on an Entity. A lock can be anything,
     * and it is up to the implementor. The Procedure Framework will call this method just before it
     * invokes {@link #execute(Object)}. It calls {@link #releaseLock(Object)} after the call to
     * execute.
     * <p/>
     * If you need to hold the lock for the life of the Procedure -- i.e. you do not want any other
     * Procedure interfering while this Procedure is running, see {@link #holdLock(Object)}.
     * <p/>
     * Example: in our Master we can execute request in parallel for different tables. We can create
     * t1 and create t2 and these creates can be executed at the same time. Anything else on t1/t2 is
     * queued waiting that specific table create to happen.
     * <p/>
     * There are 3 LockState:
     * <ul>
     * <li>LOCK_ACQUIRED should be returned when the proc has the lock and the proc is ready to
     * execute.</li>
     * <li>LOCK_YIELD_WAIT should be returned when the proc has not the lock and the framework should
     * take care of readding the procedure back to the runnable set for retry</li>
     * <li>LOCK_EVENT_WAIT should be returned when the proc has not the lock and someone will take
     * care of readding the procedure back to the runnable set when the lock is available.</li>
     * </ul>
     * @return the lock state as described above.
     */
    protected LockState acquireLock(TEnvironment env) {
        return LockState.LOCK_ACQUIRED;
    }

    /**
     * The user should override this method, and release lock if necessary.
     */
    protected void releaseLock(TEnvironment env) {
        // no-op
    }

    /**
     * Used to keep the procedure lock even when the procedure is yielding or suspended.
     * @return true if the procedure should hold on the lock until completionCleanup()
     */
    protected boolean holdLock(TEnvironment env) {
        return false;
    }

    /**
     * This is used in conjunction with {@link #holdLock(Object)}. If {@link #holdLock(Object)}
     * returns true, the procedure executor will call acquireLock() once and thereafter
     * not call {@link #releaseLock(Object)} until the Procedure is done (Normally, it calls
     * release/acquire around each invocation of {@link #execute(Object)}.
     * @see #holdLock(Object)
     * @return true if the procedure has the lock, false otherwise.
     */
    public final boolean hasLock() {
        return locked;
    }

    /**
     * Called when the procedure is loaded for replay.
     * The procedure implementor may use this method to perform some quick
     * operation before replay.
     * e.g. failing the procedure if the state on replay may be unknown.
     */
    protected void beforeReplay(TEnvironment env) {
        // no-op
    }

    /**
     * Called when the procedure is ready to be added to the queue after
     * the loading/replay operation.
     */
    protected void afterReplay(TEnvironment env) {
        // no-op
    }

    /**
     * Called when the procedure is marked as completed (success or rollback).
     * The procedure implementor may use this method to cleanup in-memory states.
     * This operation will not be retried on failure. If a procedure took a lock,
     * it will have been released when this method runs.
     */
    protected void completionCleanup(TEnvironment env) {
        // no-op
    }

    /**
     * By default, the procedure framework/executor will try to run procedures start to finish.
     * Return true to make the executor yield between each execution step to
     * give other procedures a chance to run.
     * @param env the environment passed to the ProcedureExecutor
     * @return Return true if the executor should yield on completion of an execution step.
     *         Defaults to return false.
     */
    protected boolean isYieldAfterExecutionStep(TEnvironment env) {
        return false;
    }

    /**
     * By default, the executor will keep the procedure result around util
     * the eviction TTL is expired. The client can cut down the waiting time
     * by requesting that the result is removed from the executor.
     * In case of system started procedure, we can force the executor to auto-ack.
     * @param env the environment passed to the ProcedureExecutor
     * @return true if the executor should wait the client ack for the result.
     *         Defaults to return true.
     */
    protected boolean shouldWaitClientAck(TEnvironment env) {
        return true;
    }

    /**
     * Override this method to provide procedure specific counters for submitted count, failed
     * count and time histogram.
     * @param env The environment passed to the procedure executor
     * @return Container object for procedure related metric
     */
    protected ProcedureMetrics getProcedureMetrics(TEnvironment env) {
        return null;
    }

    /**
     * This function will be called just when procedure is submitted for execution. Override this
     * method to update the metrics at the beginning of the procedure. The default implementation
     * updates submitted counter if {@link #getProcedureMetrics(Object)} returns non-null
     * {@link ProcedureMetrics}.
     */
    protected void updateMetricsOnSubmit(TEnvironment env) {
        ProcedureMetrics metrics = getProcedureMetrics(env);
        if(metrics == null) {
            return;
        }

        Counter submittedCounter = metrics.getSubmittedCounter();
        if(submittedCounter != null) {
            submittedCounter.increment();
        }
    }

    /**
     * This function will be called just after procedure execution is finished. Override this method
     * to update metrics at the end of the procedure. If {@link #getProcedureMetrics(Object)} returns
     * non-null {@link ProcedureMetrics}, the default implementation adds runtime of a procedure to a
     * time histogram for successfully completed procedures. Increments failed counter for failed
     * procedures.
     * <p/>
     * TODO: As any of the sub-procedures on failure rolls back all procedures in the stack, including
     * successfully finished siblings, this function may get called twice in certain cases for certain
     * procedures. Explore further if this can be called once.
     * @param env The environment passed to the procedure executor
     * @param runtime Runtime of the procedure in milliseconds
     * @param success true if procedure is completed successfully
     */
    protected void updateMetricsOnFinish(TEnvironment env, long runtime, boolean success) {
        ProcedureMetrics metrics = getProcedureMetrics(env);
        if(metrics == null) {
            return;
        }

        if(success) {
            Histogram timeHisto = metrics.getTimeHisto();
            if(timeHisto != null) {
                timeHisto.update(runtime);
            }
        } else {
            Counter failedCounter = metrics.getFailedCounter();
            if(failedCounter != null) {
                failedCounter.increment();
            }
        }
    }

    @Override
    public String toString() {
        // Return the simple String presentation of the procedure.
        return toStringSimpleSB().toString();
    }

    /**
     * Build the StringBuilder for the simple form of procedure string.
     * @return the StringBuilder
     */
    protected StringBuilder toStringSimpleSB() {
        final StringBuilder sb = new StringBuilder();

        sb.append("pid=");
        sb.append(getProcId());

        if(hasParent()) {
            sb.append(", ppid=");
            sb.append(getParentProcId());
        }

    /*
     * TODO
     * Enable later when this is being used.
     * Currently owner not used.
    if (hasOwner()) {
      sb.append(", owner=");
      sb.append(getOwner());
    }*/

        sb.append(", state="); // pState for Procedure State as opposed to any other kind.
        toStringState(sb);

        // Only print out locked if actually locked. Most of the time it is not.
        if(this.locked) {
            sb.append(", locked=").append(locked);
        }

        if(bypass) {
            sb.append(", bypass=").append(bypass);
        }

        if(hasException()) {
            sb.append(", exception=" + getException());
        }

        sb.append("; ");
        toStringClassDetails(sb);

        return sb;
    }

    /**
     * Extend the toString() information with more procedure details
     */
    public String toStringDetails() {
        final StringBuilder sb = toStringSimpleSB();

        sb.append(" submittedTime=");
        sb.append(getSubmittedTime());

        sb.append(", lastUpdate=");
        sb.append(getLastUpdate());

        final int[] stackIndices = getStackIndexes();
        if(stackIndices != null) {
            sb.append("\n");
            sb.append("stackIndexes=");
            sb.append(Arrays.toString(stackIndices));
        }

        return sb.toString();
    }

    protected String toStringClass() {
        StringBuilder sb = new StringBuilder();
        toStringClassDetails(sb);
        return sb.toString();
    }

    /**
     * Called from {@link #toString()} when interpolating {@link Procedure} State. Allows decorating
     * generic Procedure State with Procedure particulars.
     * @param builder Append current {@link ProcedureState}
     */
    protected void toStringState(StringBuilder builder) {
        builder.append(getState());
    }

    /**
     * Extend the toString() information with the procedure details
     * e.g. className and parameters
     * @param builder the string builder to use to append the proc specific information
     */
    protected void toStringClassDetails(StringBuilder builder) {
        builder.append(getClass().getName());
    }

    // ==========================================================================
    //  Those fields are unchanged after initialization.
    //
    //  Each procedure will get created from the user or during
    //  ProcedureExecutor.start() during the load() phase and then submitted
    //  to the executor. these fields will never be changed after initialization
    // ==========================================================================
    public long getProcId() {
        return procId;
    }

    public boolean hasParent() {
        return parentProcId != NO_PROC_ID;
    }

    public long getParentProcId() {
        return parentProcId;
    }

    public long getRootProcId() {
        return rootProcId;
    }

    public String getProcName() {
        return toStringClass();
    }

    public NonceKey getNonceKey() {
        return nonceKey;
    }

    public long getSubmittedTime() {
        return submittedTime;
    }

    public String getOwner() {
        return owner;
    }

    public boolean hasOwner() {
        return owner != null;
    }

    /**
     * Called by the ProcedureExecutor to assign the ID to the newly created procedure.
     */
    @VisibleForTesting
    protected void setProcId(long procId) {
        this.procId = procId;
        this.submittedTime = EnvironmentEdgeManager.currentTime();
        setState(ProcedureState.RUNNABLE);
    }

    /**
     * Called by the ProcedureExecutor to assign the parent to the newly created procedure.
     */
    protected void setParentProcId(long parentProcId) {
        this.parentProcId = parentProcId;
    }

    protected void setRootProcId(long rootProcId) {
        this.rootProcId = rootProcId;
    }

    /**
     * Called by the ProcedureExecutor to set the value to the newly created procedure.
     */
    @VisibleForTesting
    protected void setNonceKey(NonceKey nonceKey) {
        this.nonceKey = nonceKey;
    }

    @VisibleForTesting
    public void setOwner(String owner) {
        this.owner = StringUtils.isEmpty(owner) ? null : owner;
    }

    public void setOwner(User owner) {
        assert owner != null : "expected owner to be not null";
        setOwner(owner.getShortName());
    }

    /**
     * Called on store load to initialize the Procedure internals after
     * the creation/deserialization.
     */
    protected void setSubmittedTime(long submittedTime) {
        this.submittedTime = submittedTime;
    }

    // ==========================================================================
    //  runtime state - timeout related
    // ==========================================================================

    /**
     * @param timeout timeout interval in msec
     */
    protected void setTimeout(int timeout) {
        this.timeout = timeout;
    }

    public boolean hasTimeout() {
        return timeout != NO_TIMEOUT;
    }

    /**
     * @return the timeout in msec
     */
    public int getTimeout() {
        return timeout;
    }

    /**
     * Called on store load to initialize the Procedure internals after
     * the creation/deserialization.
     */
    protected void setLastUpdate(long lastUpdate) {
        this.lastUpdate = lastUpdate;
    }

    /**
     * Called by ProcedureExecutor after each time a procedure step is executed.
     */
    protected void updateTimestamp() {
        this.lastUpdate = EnvironmentEdgeManager.currentTime();
    }

    public long getLastUpdate() {
        return lastUpdate;
    }

    /**
     * Timeout of the next timeout.
     * Called by the ProcedureExecutor if the procedure has timeout set and
     * the procedure is in the waiting queue.
     * @return the timestamp of the next timeout.
     */
    protected long getTimeoutTimestamp() {
        return getLastUpdate() + getTimeout();
    }

    // ==========================================================================
    //  runtime state
    // ==========================================================================

    /**
     * @return the time elapsed between the last update and the start time of the procedure.
     */
    public long elapsedTime() {
        return getLastUpdate() - getSubmittedTime();
    }

    /**
     * @return the serialized result if any, otherwise null
     */
    public byte[] getResult() {
        return result;
    }

    /**
     * The procedure may leave a "result" on completion.
     * @param result the serialized result that will be passed to the client
     */
    protected void setResult(byte[] result) {
        this.result = result;
    }

    /**
     * Will only be called when loading procedures from procedure store, where we need to record
     * whether the procedure has already held a lock. Later we will call
     * {@link #restoreLock(Object)} to actually acquire the lock.
     */
    final void lockedWhenLoading() {
        this.lockedWhenLoading = true;
    }

    /**
     * Can only be called when restarting, before the procedure actually being executed, as after we
     * actually call the {@link #doAcquireLock(Object, ProcedureStore)} method, we will reset
     * {@link #lockedWhenLoading} to false.
     * <p/>
     * Now it is only used in the ProcedureScheduler to determine whether we should put a Procedure in
     * front of a queue.
     */
    public boolean isLockedWhenLoading() {
        return lockedWhenLoading;
    }

    // ==============================================================================================
    //  Runtime state, updated every operation by the ProcedureExecutor
    //
    //  There is always 1 thread at the time operating on the state of the procedure.
    //  The ProcedureExecutor may check and set states, or some Procecedure may
    //  update its own state. but no concurrent updates. we use synchronized here
    //  just because the procedure can get scheduled on different executor threads on each step.
    // ==============================================================================================

    /**
     * @return true if the procedure is in a RUNNABLE state.
     */
    public synchronized boolean isRunnable() {
        return state == ProcedureState.RUNNABLE;
    }

    public synchronized boolean isInitializing() {
        return state == ProcedureState.INITIALIZING;
    }

    /**
     * @return true if the procedure has failed. It may or may not have rolled back.
     */
    public synchronized boolean isFailed() {
        return state == ProcedureState.FAILED || state == ProcedureState.ROLLEDBACK;
    }

    /**
     * @return true if the procedure is finished successfully.
     */
    public synchronized boolean isSuccess() {
        return state == ProcedureState.SUCCESS && !hasException();
    }

    /**
     * @return true if the procedure is finished. The Procedure may be completed successfully or
     *         rolledback.
     */
    public synchronized boolean isFinished() {
        return isSuccess() || state == ProcedureState.ROLLEDBACK;
    }

    /**
     * @return true if the procedure is waiting for a child to finish or for an external event.
     */
    public synchronized boolean isWaiting() {
        switch(state) {
            case WAITING:
            case WAITING_TIMEOUT:
                return true;
            default:
                break;
        }
        return false;
    }

    @VisibleForTesting
    protected synchronized void setState(final ProcedureState state) {
        this.state = state;
        updateTimestamp();
    }

    public synchronized ProcedureState getState() {
        return state;
    }

    protected void setFailure(final String source, final Throwable cause) {
        setFailure(new RemoteProcedureException(source, cause));
    }

    protected synchronized void setFailure(final RemoteProcedureException exception) {
        this.exception = exception;
        if(!isFinished()) {
            setState(ProcedureState.FAILED);
        }
    }

    protected void setAbortFailure(final String source, final String msg) {
        setFailure(source, new ProcedureAbortedException(msg));
    }

    /**
     * Called by the ProcedureExecutor when the timeout set by setTimeout() is expired.
     * <p/>
     * Another usage for this method is to implement retrying. A procedure can set the state to
     * {@code WAITING_TIMEOUT} by calling {@code setState} method, and throw a
     * {@link ProcedureSuspendedException} to halt the execution of the procedure, and do not forget a
     * call {@link #setTimeout(int)} method to set the timeout. And you should also override this
     * method to wake up the procedure, and also return false to tell the ProcedureExecutor that the
     * timeout event has been handled.
     * @return true to let the framework handle the timeout as abort, false in case the procedure
     *         handled the timeout itself.
     */
    protected synchronized boolean setTimeoutFailure(TEnvironment env) {
        if(state == ProcedureState.WAITING_TIMEOUT) {
            long timeDiff = EnvironmentEdgeManager.currentTime() - lastUpdate;
            setFailure("ProcedureExecutor", new TimeoutIOException("Operation timed out after " + StringUtils.humanTimeDiff(timeDiff)));
            return true;
        }
        return false;
    }

    public synchronized boolean hasException() {
        return exception != null;
    }

    public synchronized RemoteProcedureException getException() {
        return exception;
    }

    /**
     * Called by the ProcedureExecutor on procedure-load to restore the latch state
     */
    protected synchronized void setChildrenLatch(int numChildren) {
        this.childrenLatch = numChildren;
        if(LOG.isTraceEnabled()) {
            LOG.trace("CHILD LATCH INCREMENT SET " + this.childrenLatch, new Throwable(this.toString()));
        }
    }

    /**
     * Called by the ProcedureExecutor on procedure-load to restore the latch state
     */
    protected synchronized void incChildrenLatch() {
        // TODO: can this be inferred from the stack? I think so...
        this.childrenLatch++;
        if(LOG.isTraceEnabled()) {
            LOG.trace("CHILD LATCH INCREMENT " + this.childrenLatch, new Throwable(this.toString()));
        }
    }

    /**
     * Called by the ProcedureExecutor to notify that one of the sub-procedures has completed.
     */
    private synchronized boolean childrenCountDown() {
        assert childrenLatch > 0 : this;
        boolean b = --childrenLatch == 0;
        if(LOG.isTraceEnabled()) {
            LOG.trace("CHILD LATCH DECREMENT " + childrenLatch, new Throwable(this.toString()));
        }
        return b;
    }

    /**
     * Try to set this procedure into RUNNABLE state.
     * Succeeds if all subprocedures/children are done.
     * @return True if we were able to move procedure to RUNNABLE state.
     */
    synchronized boolean tryRunnable() {
        // Don't use isWaiting in the below; it returns true for WAITING and WAITING_TIMEOUT
        if(getState() == ProcedureState.WAITING && childrenCountDown()) {
            setState(ProcedureState.RUNNABLE);
            return true;
        } else {
            return false;
        }
    }

    protected synchronized boolean hasChildren() {
        return childrenLatch > 0;
    }

    protected synchronized int getChildrenLatch() {
        return childrenLatch;
    }

    /**
     * Called by the RootProcedureState on procedure execution.
     * Each procedure store its stack-index positions.
     */
    protected synchronized void addStackIndex(final int index) {
        if(stackIndexes == null) {
            stackIndexes = new int[]{index};
        } else {
            int count = stackIndexes.length;
            stackIndexes = Arrays.copyOf(stackIndexes, count + 1);
            stackIndexes[count] = index;
        }
    }

    protected synchronized boolean removeStackIndex() {
        if(stackIndexes != null && stackIndexes.length > 1) {
            stackIndexes = Arrays.copyOf(stackIndexes, stackIndexes.length - 1);
            return false;
        } else {
            stackIndexes = null;
            return true;
        }
    }

    /**
     * Called on store load to initialize the Procedure internals after
     * the creation/deserialization.
     */
    protected synchronized void setStackIndexes(final List<Integer> stackIndexes) {
        this.stackIndexes = new int[stackIndexes.size()];
        for(int i = 0; i < this.stackIndexes.length; ++i) {
            this.stackIndexes[i] = stackIndexes.get(i);
        }
    }

    protected synchronized boolean wasExecuted() {
        return stackIndexes != null;
    }

    protected synchronized int[] getStackIndexes() {
        return stackIndexes;
    }

    // ==========================================================================
    //  Internal methods - called by the ProcedureExecutor
    // ==========================================================================

    /**
     * Internal method called by the ProcedureExecutor that starts the user-level code execute().
     * @throws ProcedureSuspendedException This is used when procedure wants to halt processing and
     *           skip out without changing states or releasing any locks held.
     */
    protected Procedure<TEnvironment>[] doExecute(
            TEnvironment env) throws ProcedureYieldException, ProcedureSuspendedException, InterruptedException {
        try {
            updateTimestamp();
            if(bypass) {
                LOG.info("{} bypassed, returning null to finish it", this);
                return null;
            }
            return execute(env); // TODO 核心代码

        } finally {
            updateTimestamp();
        }
    }

    /**
     * Internal method called by the ProcedureExecutor that starts the user-level code rollback().
     */
    protected void doRollback(TEnvironment env) throws IOException, InterruptedException {
        try {
            updateTimestamp();
            if(bypass) {
                LOG.info("{} bypassed, skipping rollback", this);
                return;
            }
            rollback(env);
        } finally {
            updateTimestamp();
        }
    }

    final void restoreLock(TEnvironment env) {
        if(!lockedWhenLoading) {
            LOG.debug("{} didn't hold the lock before restarting, skip acquiring lock.", this);
            return;
        }

        if(isFinished()) {
            LOG.debug("{} is already finished, skip acquiring lock.", this);
            return;
        }

        if(isBypass()) {
            LOG.debug("{} is already bypassed, skip acquiring lock.", this);
            return;
        }
        // this can happen if the parent stores the sub procedures but before it can
        // release its lock, the master restarts
        if(getState() == ProcedureState.WAITING && !holdLock(env)) {
            LOG.debug("{} is in WAITING STATE, and holdLock=false, skip acquiring lock.", this);
            lockedWhenLoading = false;
            return;
        }
        LOG.debug("{} held the lock before restarting, call acquireLock to restore it.", this);
        LockState state = acquireLock(env);
        assert state == LockState.LOCK_ACQUIRED;
    }

    /**
     * Internal method called by the ProcedureExecutor that starts the user-level code acquireLock().
     */
    final LockState doAcquireLock(TEnvironment env, ProcedureStore store) {
        if(waitInitialized(env)) {
            return LockState.LOCK_EVENT_WAIT;
        }
        if(lockedWhenLoading) {
            // reset it so we will not consider it anymore
            lockedWhenLoading = false;
            locked = true;
            // Here we return without persist the locked state, as lockedWhenLoading is true means
            // that the locked field of the procedure stored in procedure store is true, so we do not need
            // to store it again.
            return LockState.LOCK_ACQUIRED;
        }
        LockState state = acquireLock(env);
        if(state == LockState.LOCK_ACQUIRED) {
            locked = true;
            // persist that we have held the lock. This must be done before we actually execute the
            // procedure, otherwise when restarting, we may consider the procedure does not have a lock,
            // but it may have already done some changes as we have already executed it, and if another
            // procedure gets the lock, then the semantic will be broken if the holdLock is true, as we do
            // not expect that another procedure can be executed in the middle.
            store.update(this);
        }
        return state;
    }

    /**
     * Internal method called by the ProcedureExecutor that starts the user-level code releaseLock().
     */
    final void doReleaseLock(TEnvironment env, ProcedureStore store) {
        locked = false;
        // persist that we have released the lock. This must be done before we actually release the
        // lock. Another procedure may take this lock immediately after we release the lock, and if we
        // crash before persist the information that we have already released the lock, then when
        // restarting there will be two procedures which both have the lock and cause problems.
        if(getState() != ProcedureState.ROLLEDBACK) {
            // If the state is ROLLEDBACK, it means that we have already deleted the procedure from
            // procedure store, so do not need to log the release operation any more.
            store.update(this);
        }
        releaseLock(env);
    }

    @Override
    public int compareTo(final Procedure<TEnvironment> other) {
        return Long.compare(getProcId(), other.getProcId());
    }

    // ==========================================================================
    //  misc utils
    // ==========================================================================

    /**
     * Get an hashcode for the specified Procedure ID
     * @return the hashcode for the specified procId
     */
    public static long getProcIdHashCode(long procId) {
        long h = procId;
        h ^= h >> 16;
        h *= 0x85ebca6b;
        h ^= h >> 13;
        h *= 0xc2b2ae35;
        h ^= h >> 16;
        return h;
    }

    /**
     * Helper to lookup the root Procedure ID given a specified procedure.
     */
    protected static <T> Long getRootProcedureId(Map<Long, Procedure<T>> procedures, Procedure<T> proc) {
        while(proc.hasParent()) {
            proc = procedures.get(proc.getParentProcId());
            if(proc == null) {
                return null;
            }
        }
        return proc.getProcId();
    }

    /**
     * @param a the first procedure to be compared.
     * @param b the second procedure to be compared.
     * @return true if the two procedures have the same parent
     */
    public static boolean haveSameParent(Procedure<?> a, Procedure<?> b) {
        return a.hasParent() && b.hasParent() && (a.getParentProcId() == b.getParentProcId());
    }
}
